(1) Field of the Invention
This invention relates to a change-speed apparatus in a tractor, provided with a planetary gearing mechanism to function as a two-step speed shifter.
(2) Description of the Prior Art
As has conventionally been the case, when a tractor is equipped with a change-speed apparatus provided in turn with a planetary gearing mechanism and with a hydraulically operated clutching assembly, wherein the planetary gearing mechanism has: a ring gear operatively connected to a driving shaft; a carrier, journaling thereon planetary gears in meshing with the ring gear, operatively connected to an output shaft; and a sun gear in meshing with the planetary gears, shiftable between an inactive transmission maneuvering position of being let to freely and idly rotate without bearing any transmission load and an active transmission maneuvering position of being consolidated with a stationary mass thus of being blocked against rotation as so hydraulically power-actuated with intermediary of the said clutching assembly which is supplied with the working oil pressurized by a pump driven by the engine power; there has been a problem, when the engine is stopped for instance during the parking, in that the said working oil pressure accordingly comes to extinction to therefore bring the clutching assembly into said inactive transmission maneuvering position thus ruining and incapacitating the function of the engine brake as would be expected if the engine piston as inversely driven from the wheels tending inadvertently to move should show effective resisting effort against such forcible inverse driving, since in the said conventional case of the inactive transmission the inverse driving by such wheels, tending to move for instance on a slant, can reach back indeed up to the output shaft of the clutching assembly but the output shaft, consolidated with the carrier, then rotates idly without effectively transmitting any power back to the ring gear and further to the engine as it only causes the idle sun gear to freely rotate.